الفهرس 
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Abstract
Development of reliability assessment techniques and programs is very important in power system planning and testing of existing power network configu~ation for detecting its weak points. The development and utilization of a reliability program are greatly influenced by experience of a utility and the intent of the system manager, planner and designer conducting the reliability studies. The reliability studies of bulk power system indicate the ability of the composite generation and transmission system to satisfy the load demand at the major load points. Considerable effort has been applied over the last two decades to develop techniqucs and criteria for adequacy evaluation of composite power systems. A major
. burden in the developed methods, used in evaluation of large composite system reliability, is the computation time required to solve a large number
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of credible contingencies or outages ..
The use of historical data and heuristic methods are inadequate for determining how reliable a system is. They also poorly explain the characteristics of the system such as age, location, climate and exposure to trees. A fuzzy reasoning approach may explain these factors better than traditional methods because it docs not rely on historical data which may not be available or accurate and it provides a rating method from 0 to I for the relative reliability of systems.
Power system reliability problem is a multi-objective problem. The evaluation of such problem is very complicated and requires a large scale of time. Implementation of fuzzy concepts in evaluating the powcr systcm reliability is then introduced. For realistic modeling it is useful to consider
three states of the system in which the wear-out period is taken into account by a pending-failure state. A 3-state component has been considered in the proposed algorithm. Fuzzy probabilities were used to define the coefficients of different terms in the trinomial reliability expression. The trinomial reliability coefficients are composed of global cutsets, which reflect link importance of the system. Th~ proposed algorithm is useful to reduce the
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problem complexity, which is polynomial and has been considered very
simple relative to others. It is simple to calculate the system reliability according to system loss of continuity whether it is total or partial. The entire logic of the algorithm is explained in details and verified through numerical examples. Included results of a larger system show that the algorithm is appreciably faster than previous algorithms, and can handle much larger graphs due to less memory requirements.